<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer {
            border: 5px solid red;
            /* float: left; */
            /* overflow: auto; */
            overflow: hidden;
        }
        
        .inner {
            width: 200px;
            height: 200px;
            border: 3px solid green;
            background-color: #bfa;
            float: left;
        }
        
        .test {
            width: 200px;
            height: 200px;
            background-color: blue;
        }
    </style>
</head>

<body>
    <div class="outer">
        <div class="inner">

        </div>
        <div class="inner">

        </div>
    </div>
    <div class="test">

    </div>
</body>

</html>